Process of rendering paper transparent



c. E. SWETT PROCESS OF BENDERI NG PAPER TRANSPARENT Jan. 19,1926..1570;098'

Filed May 18,- 1922 liarra K071 6'72an8es Z a/e22 Patented Jan. 19,1926.

UNITED STATES PATENT OFFICE.

CHARLES E. SWETT, OF "WEST ROXBURY, MASSACHUSETTS, ASSIGNOR TO UNITEDSTATES ENVELOPE COMPANY,- OF SPRINGFIELD, MASSACHUSETTS, A. CORPORA-TION OF MAINE.

PROCESS OF RENDERING PAPER TRANSPARENT.

Application filed May is;

To all whom it may concern.-

Be it known that I, CHARM-1s E. SWE'LT,

a citizen of the United States, residing at West Roxbury, in the countyof Suffolk and 5 Commonwealth of ,Massachusctts. have in-- vented a newand useful Improvement in a Process of Rendering Paper Transparent, ofwhich the following is a specification.

The present invention relates to improvements in the art of treatingpaper, for the purpose of rendering it transparent. The process isapplicable, for instance, to the manufacture of window envelopes of theone piece type, i. e., anenvelope in which an integral part of thematerial is made pervious to light by treatment with a suitablesubstance of a resinous or similar nature.

The invention resides in a certain mode of treatment adapted to decreasevery materially the time required for completing the transparentizingoperation and for bringing the treated blanks or sheets into conditionfor subsequent operations thereon, such as printing, stacking, foldingand the like. In consequence of this, as hereinafter described, it ispossible, by the use of the invention, to coordinate, and to perform ina practically continuous manner, the several successive operationsrequired for the production of the finished articles.- without need forany substantial interruption in the entire manufacturing process frombeginning to end.

It is well known that the impregnation of paper with various suitablesubstances of a resinous or similar nature operates, to a greater orless degree. in making the material pervious to light, or transparent;and it is also recognized that for permanence of result, theimpregnating substance should remain in the paper in the formsubstantially of a solid. In the utilization of these principles, thepractice, in general, has been to use a solvent for the resinous orsimilar matter, the liquid mixture being applied to the aper and causedto penetrate its pores; tliereafter, by driving off the solvent anddrying the residue, the desired 50 result is obtained.

Heretofore, it has been deemed essential A and indispensable to' theabove described process that the sheets or blanks of paper,

following the application of the treating 1922. Serial No. 562,030.

sheets or blanks'are to be subjected. For.

example, in the manufacture of one piece window envelopes, thistransparentizing treatment has heretofore been available only as anindependent preliminary operation, separate and apart from the othermanufacturing steps; the envelope blanks, after application thereto ofthe treating liquid,

have to be spread out by hand on trays, to

facilitate their disposal in a suitable oven or heating chamber, andthen, following the prolonged heating of the treated blanks, they haveto be handled a second time, in order to assemble them into stacks,preparatory to their passage through an envelope folding machine.

I have discovered that the above described prolonged application of heatcan be dispensed with in the process of transparentizing paper. In theaccompanying drawing, the single figure represents, diagrammatically,one form of apparatus which may be used in putting my invention intoeffect, as hereinafter described. According to my invention. the sheetsor blanks, having received their imprints or coatings of the treatingliquid. are subjected to alternate short periods of heating and cooling,the aggregate duration of which for the entire process need not, underordinary circumstances. exceed two minutes,in contrast with the muchlonger'period, usually an hour or more. that is required when theheating is uninterrupted.

The invention resides essentially in the above described mode oftreatment, without regard to the mechanism or apparatus employed forperforming the same,since it is obvious that the process is susceptibleof utilization in a large variety of ways, as for instance, by causingthe treated material, in its progress, either continuous orintermittent, towards those instrumentalities which convert it into thefinished product, to par:

on an endless conveying belt 1, for example, through alternate hot andcold zones, the former being constituted, for example, by heated platesor coils, 2, 2, and the latter either by the unheated intervening spacesor by blasts of air 3, 3 directed onto the material in the intervalsbetween its subjections to heat. I Y

The limits and proportions of time and temperature, and also the numberand duration of the alternate heating and cooling cycles will vary, forthe different conditions and requirements that arise,all of, the abovebeing affected in greater or less degree by such factors as thethickness of the paper, and its condition" as to moisture ll1nmaterials, sizing and the like, and also y the composition of thetreating sub stance. In general, it is found advantageous to give theheating periods a slightly longer duration that the alternatecoolingperiods, and also to subject the pa er in said heating periods tosomewhat igher temperatures than those that are reached when rolongedand uninterrupted heating, accord ing to previous known processes, isemployed; this last can be done, without damage to the paper, becausethebeatings are of such short duration. This treatment, giving acceleratedimpregnation to the paer, coupled with recurring o ortunities .or thecondensation and soli i cation of the transparentizing substance, needonly be continued for a very short time; its

culmination finds the. sheets or blanks in condition for immediatefurther operations thereon,the impregnated portions thereof havinghardened and dried sufficiently to permit stacking of the sheets orblanks, without danger of sticking. As applied for instance to themanufacture of one piece window envelopes, the invention, by eliminatingthe necessity for prolonged transarentizing treatment, permits saidmanu-- iods of s ort duration to obtain accelerated v penetration andsolidification of the impregnating substance.

2. In the art of rendering aper transparent, the improvement whlcliconsists in applying to the paper an impregnating substance, andheating, the paper at intervals, alternately with ex osures toatmospheric temperature, to obta1n solidification of said impregnatingsubstance.

ated this 16th day of May, 1922.

CHARLES E. swam,

